1. Field of the Invention
The present invention relates to a wireless mobile communication system. More particularly, the present invention relates to an apparatus and method for transmitting and receiving a signal on the basis of Hybrid Automatic Repeat reQuest (HARQ) in a wireless mobile communication system.
2. Description of the Related Art
Wireless mobile communication systems are being developing to provide various services such as broadcasting, multimedia video, multimedia message services, etc. In particular, next-generation wireless mobile communication systems are being developed to provide a data service of at least 100 Mbps to users moving at high speed and to provide a data service of at least 1 Gbps to users moving at low speed.
The above-described wireless mobile communication systems require the reduction of system overhead and short latency so that a base station and a mobile station can transmit and receive data reliably and at high speed. A synchronous HARQ may be considered as one method for reducing the system overhead and supporting short latency. Since initial transmission and subsequent retransmission are performed according to a predefined cycle, the synchronous HARQ has a regular retransmission delay. Accordingly, the synchronous HARQ has a given correspondence relation between initial transmission timing and retransmission timing. This correspondence relation is called HARQ interlace. That is, the HARQ interlace indicates that a relation between a time slot in which resource allocation information (that is, a MAP message) indicating resources allocated to data transmission and a time slot in which data is transmitted according to the MAP message, a relation between a time slot in which the data is transmitted and a time slot in which a feedback corresponding to the data is transmitted, and a relation between a time slot in which the feedback is transmitted and a time slot in which data corresponding to the feedback is transmitted or retransmitted are prescribed regularly.
In a wireless mobile communication system using the above-described HARQ scheme, a transmitter transmits a signal including data and then a receiver transmits a positive response (i.e. ACKnowledge (ACK)) or a negative response (i.e. Not ACKnowledge (NACK)) to the transmitter according to whether the data has been received normally. The transmitter end transmits new data according to the reception of ACK or NACK or retransmits previously transmitted data according to the HARQ. Here, the HARQ scheme indicates a Chase Combining (CC) or Incremental Redundancy (IR) scheme. As described above, the HARQ scheme results in time delays such as a transmission delay when the transmitting end transmits new data according to the reception of ACK after data transmission and a retransmission delay when the transmitter retransmits the data according to the reception of NACK after data transmission.
When the retransmission delay is maintained regularly in the communication system using the above-described HARQ scheme, the base station may use a continuous allocation method. The continuous allocation method enables the mobile station to repeatedly use first allocated resources at the same position within each frame during a given time interval, thereby omitting the transmission of a control message indicating resource allocation at each data transmission or retransmission time or reducing the number of control message transmissions. However, a delay time due to the retransmission delay may vary with a ratio between the number of DownLink (DL) time slots and the number of UpLink (UL) time slots. Here, the time slot indicates a unit of resource allocation determined by a predetermined time interval and/or frequency band.
In contrast, the communication system must support the transmission of various types of data bursts according to a service state or capability of the base station or mobile station. For example, when a channel state is good for at least a predetermined standard, a data burst of at least a predetermined size is transmitted during a relatively long transmission interval to satisfy a high data rate. When the channel state is bad for less than the predetermined standard, a data burst of less than the predetermined size is transmitted during a relatively long transmission interval to ensure robust data burst transmission.
A node having low processing capability requires a relatively long processing time at the time of signal transmission/reception, and a node having high processing capability requires a relatively short processing time for signal transmission/reception. Here, the processing time may be a reception processing time required to demodulate and decode received data so that the receiver feeds back a result of error detection for the received data and a transmission processing time required to perform scheduling/encoding so that the transmitter retransmits/initially transmits after detection of ACK/NACK.
Therefore, there is a need for an adaptive HARQ interlace method capable of processing a signal by considering various situations such as various lengths of data burst transmission intervals, capabilities of a base station and a mobile station, etc.